Refrigerating apparatus



March 1959 s. R. PRANCE IETAL 2,878,659

REFRIGERATING APPARATUS Filed July 15, 1955 INVENTORS 7 Stanley R. France y Harry 0. W00

Their A/forney United States REFRIGERATING APPARATUS Application July 15, 1955,. Serial No. 522,215 2 Claims. (162-357 This invention relates to ice trays and is particularly directed to mechanical ice trays having superior ice shedding properties and to methods of making said trays.

It is the main object of the invention to provide an ice tray assembly with a water repellent coating which completely covers the tray and its grid, and facilitates the shedding of ice from the tray.

Another object of the invention is to provide a mechanical ice tray, of the type which includes mechanism for flexing the grid to facilitate the shedding of ice therefrom, with a coating thereover of a permanently associated material which has low adhesion properties with respect to ice, such material being known as polytetrafluoroethylene.

Another object of the invention is to provide an ice tray and grid of aluminum or aluminum alloy, cast or sheet having fully anodized surfaces upon which is adhered and coated a polytetrafluoroethylene covering in a thickness in the order of from .3 mil to 1.3 mi1s.

Another object of the invention is to provide an aluminum or aluminum alloy ice tray and grid therefor, wherein the metal'surfaces of the tray and grid are coated and covered with an abrasion resistant, water repellent, longwearing coating material which reduces the adhesion of ice to surfaces of the tray and grid, thereby facilitating the shedding of ice therefrom, such coating material being polytetrafluoroethylene, which is sold under the trade name of Teflon.

Another object of the invention is to provide a method for coating the surface of a metal ice tray which comprises etching the surface of the tray that is to be coated, applying polytetrafluoroethylene in suspended particle form in a liquid vehicle to said etched surface in sufficient quantities to subsequently provide a layer having an average depth of from .30 to 1.3 mils, evaporating said vehicle at a temperature below 300 F., heating the tray with the applied polytetrafluoroethylene thereon to a temperature above the fusion temperature of the polytetrafluorethylene and below the vaporization temperature thereof to cause the polytetrafluoroethylene to fuse onto the etched surface of the metal tray for forming a coextensive layer thereover and finally cooling the tray with the coating thereon.

, Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the invention is clearly shown.

In the drawing:

Figure l is a fragmentary view in perspective of an ice tray and grid therefor of conventional design; and

Figure 2 is a fragmentary sectional view on an enlarged scale taken on line 2--2 of Figure 1.

Metal ice trays of various types, for example as disclosed in-U.S. Patents 2,516,257, 2,615,310 and 2,642,- 727, have been used wherein the tray or its grid or both have been flexible or mechanically operable to break the ice cubes loose therefrom. In order to facilitate this operation, it has been conventional practice to coat the surfaces of the tray and grid which come into contact with atent O "ice a water repellent coating which has a low degree of adhesion to ice. Such coatings have been waxes-of various types and mixtures. The use of the wax reduces the adhesion of the ice to the metal parts to such a degree that mechanical flexing of the tray and/or grid is' a relatively easy matter whereby the ice cubes are shedfrom the coated metal parts of the tray.

One of the failings of wax coated ice trays is the-relatively short life of the wax coating. This coating is brittle in character when cold and if the tray is flexed appreciably, some of the wax coating tends to flake oif'and furthermore when the tray has been in use over an extended period of time, the wax coating wears off. Further, the wax is softened and removed by hot water and detergents used in washing the tray. Thus, during use of the tray, the adhesion of the ice cubes to'the tray and grid progressively increases, requiring increasing force to cause ejection or shedding thereof. Eventually, all of the wax which is effective in aiding the shedding operation has been worn off, whereupon it is very difficult, if not impossible, to mechanically shed the ice from the tray and grid. In these instances, the user must resort to the old practice of running hot water on the tray to partly melt the ice so that the cubes may be removed from the tray.

The present invention is directed to a tremendous advance in the processing of ice trays and grids wherein a coating is applied thereto which is coextensive and which, due to its very physical characteristics does not wear off or flake off, is abrasion-resistant, corrosion-resistant, is unaffected by hot water or detergents and isnon-toxic in character. Furthermore, the material, due to its somewhat waxy nature, is ideal for reducing the adhesion of ice to metal whereby the tray will easily shed the ice cubes therefrom throughout the life of the tray. This is a marked improvement over prior art ice trays and receptacles since the mechanism of the tray always requires substantially the same application of force in order to shed the cubes and therefore the mechanical device used to operate the tray is not injured due to heavy forces being applied thereto as in the past and likewise, the coating material remains on the tray throughout its life and thus presents an article which does not need frequent replacement. Further, due to the continued life and effectiveness of the coating, it is possible to manufacture the tray and grid of lighter material since undue strains are never imposed on the mechanism due to wearing off of the coating as in the case of prior art trays.

Specifically, we have found that by properly processing an ice tray 20 and grid 22 therefor, it is possible to apply coating 24 of polytetrafluoroethylene thereto which tenaciously adheres to the metal surfaces of the tray and completely covers all metal surfaces thereof and which, due to its abrasion resistance and slight degree of resilience, has no tendency to wear or flake off the surfaces of the tray.

In the processing of ice trays and grids, we first chemically clean the alumimun tray and grid and then anodize the surface thereof to provide a finely etched surface, the anodizing is done by conventional anodizing processes for aluminum as clearly shown in Patent No. 1,891,703. The aluminum part, whether it be the tray or grid or both, is then washed and the surface thereof is treated with polytetrafluoroethylene. This is done in either one of two ways, first, the polytetrafiuoroethylene is mixed with water preferably distilled and is sprayed over the surface in the form of a low viscosity dispersion. The thickness of the polytetrafluoroethylene coating deposited on the surface of the metal is partly controlled by the density of the dispersion, that is to say,

by the amount of polytetrafluoroethylene in suspension the coating suspension.

in thickness up to 1 mil.

in the vehicle. Also the thickness of the final coating may be controlled by the use of multiple coating operations in order to build up the thickness of polytetrafluoroethylene that is deposited on the surface to a desired thickness. A :desired thickness is preferably in the order of from .3 mil to 1.3 mils. In place of spraying, brushing, .dipping or flow coating may be used and in each case, the suspension density should be adjusted to yield adesired thickness of coating. It is apparent here that coatings of appreciable thickness are undesirable, both from a cost standpoint and because of the lowering of elasticity nor resilience of the coating after final processing.

In practice, Teflon particles preferably in the form of a finely divided powder, are suspended in water to form the coating mixture. To this suspension may be added a relatively small quantity of a suitable agent to prove adherence of the coating material to the metal to which it is to .be subsequently applied. This addition may take the form of chromic acid or any other suitable oxidizing acids if desired.

It :may also be useful to include a wetting agent in Non-ionic wetting agents taken from the class of alkyl aryl polyether alcohols are suitable :for this purpose and generally enhance the covering or coating qualities of the material as it is applied to the metal surfaces.

Also, other vehicles may be used for the Teflon. For example, more volatile materials such as organic materials taken from the class consisting of benzene, toluene and xylene either alone or in admixture with one another or with other vehicles well known in the art may be used.

It is to be understood that the particular coating mixture may be varied widely without departing from the spirit of our invention which basically comprises forming a covering of Teflon over the operating and etched surfaces of the tray and/or its grid so as to reduce the adhering tendency of ice thereto so that the ice maybe readily shed therefrom.

After the coating is applied to the part, the coating is dried at a suitable temperature ranging from room temperature to about 200 F. with the time required for drying varying inversely with temperature. After the coating has been dried, it is then baked at a temperature of about 750 in air. Temperatures below 680 are not recommended whereas temperatures in the range of 700 F. to 750 F. are preferred. In order to prevent blistering of the coating due to too rapid evaporation of the water during the first drying step, it is preferable to use a-gradual step-up in temperature or a two-stage heating process if a maximum of 200 F. to 300 F. is contemplated. In this manner, a large portion of the water is evaporated prior to the final drying.

It is also possible to apply the coating in a two step process wherein a primer coat is used which is carried out with very low viscosity material, which coating in a thickness of about .3 mil is dried and cured as above noted, after which a second layer is applied to the part In all cases, the spraying is done with a conventional De Vilbiss type gun using air pressures in the order of 25 to 45 pounds with fluid feed pressures ranging from one to five pounds. Any comparable apparatus will be satisfactory for the spraying operation.

The curing period in the order of 750 F. will vary in accordance with the thickness of the metal being coated and the thickness of the film. It is only necessary to actually fuse or sinter the film in order to assure adequate cure. In actual practice a cure of about eight minutes at 750 F. yields satisfactory results in connection'with conventional ice trays having a metal thickness in the order of .050 inch to .062 inch. In all cases the cure should be suflicient to produce an adhering, coextensive film or layer over the entire surface of the part being treated. During'this fusing step, it is believed that fluorine compounds are emitted so that adequate ventilation must be provided during this portion of the treatment. After the cure is completed, it is preferable to quench the finished article in cold water since the quench produces a better transparency and tougher coatings. In the case of the multiple coating operation, multiple quenches may be used if desired. In all cases pigments may be added to the coating material if desired.

It is apparent that since the fusing of the coating is carried out at temperatures in the order of 750 F., the coating is very resistant toward high temperatures which is a useful factor in ice trays since such trays are frequently washed in hot water which tends to soften and often remove the conventional wax coatings whereas hot water will in no way atfect the present coating of polytetrafluoroethylene. Similarly, the coating is very resistant toward the action of various chemicals used in washing, such as the common household detergents. ,Here

again these same detergents have a deleterious eflect on wax coatings.

It is apparent therefore that this improved ice tray combination eliminates many of the problems apparent in ice trays of the past, while .providing a coating which will last throughout the life of the ice tray without any noticeable reduction in efficiency toward the shedding of We believe that one of the reasons behind the phenomenal success of the coating of polytetrafluoroethylene as an ice shedding material is its wear resistant and abrasion resistant qualities. In the usual mechanical ice tray the grid member is mechanically operated to cause the cross grid walls or partitions to move relative to the longitudinal wall. In so doing the partitions abrade the longitudinal wall and in the case of waxed ice trays readily scrape off the wax coating whereby, after even a single operation of the grid, the longitudinal wall has a high degree of adherence to the ice blocks or cubes-due to the fact that substantial portions thereof do not have a coextensive water repellent coating thereon. .In the case of polytetrafluoroethylene, the coating is tenaciously bonded to the etched surface of the metal and due to the .wear and abrasion resistant qualities of the coating material resists scraping off or abrasion by the cross walls or partition members. For these reasons the longitudinal member remains coextensively coated by the Teflon envelope and thereby reduces the pull necessary to operate the tray for ejecting or shedding the ice therefrom. Thus, a mechanical ice tray coated with Teflon normally requiresless pull to opcrate the same than the same tray coated with one of the usual waxy compounds and furthermore, the Teflon coated tray continues to be operable under substantially constant conditions of applied force while the usual wax coated tray requires ever increasing applied force to eject the cubes therefrom.

It is also manifest that in place of aluminum or its alloys, stainless steel, nickel or other materials may be used in the tray and/ or grid construction. In the case of metals other than aluminum, an acid etch is desirable to improve adherence.

While the forms of embodiment of the invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. An ice tray assembly comprising in combination, a metal tray member and a metal grid member adapted to be fitted therein and carried thereby,portions at least of the surface of each of said members being etched to produce a roughened surface, and a solid, tough, and heat resistant coating material having good ice shedding properties coextensively covering the etched surface portions of said tray and grid members and strongly bonded thereto, said coating material consisting of fused and quenched polytetrafluoroethylene having a thickness from .3 mil to 1.3 mils.

2. An ice tray assembly comprising in combination, a tray member and a grid member adapted to be fitted therein and removably carried thereby wherein said tray and grid members are formed from a metal taken from the class consisting of sheet aluminum, cast aluminum, stainless steel, nickel and alloys thereof and wherein the metal surfaces of said members are etched, and a solid, tough, and heat resistant coating envelope having good ice shedding properties coextensively covering the etched metal surfaces of said members and tenaciously bonded thereto, said coating envelope consisting essentially of a coextensive covering of fused and quenched polytetrafluoroethylene having an average thickness ranging between .3 mil and 1.3 mils.

6 References Cited in the file of this patent UNITED STATES PATENTS 

